Microwave plasma source and plasma processing apparatus

ABSTRACT

There are provided a microwave plasma source and a plasma processing apparatus capable of improving uniformity of a plasma density distribution within a processing chamber by controlling positions of nodes and antinodes of a standing wave of microwave within the processing chamber not to be fixed. The microwave plasma source  2  includes a microwave supply unit  40.  The microwave supply unit  40  includes multiple microwave introducing devices  43  each introducing microwave into the processing chamber; and multiple phase controllers  46  for adjusting phases of the microwaves inputted to the microwave introducing devices  43.  Here, the phases of the microwaves inputted to the microwave introducing devices  43  are adjusted by fixing an input phase of the microwave inputted to one of two adjacent microwave introducing devices  43  while varying an input phase of the microwave inputted to the other microwave introducing device  43  according to a periodic waveform.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No. 2010-234688 filed on Oct. 19, 2010, the entire disclosures of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present disclosure relates to a microwave plasma source and a plasma processing apparatus using the same.

BACKGROUND OF THE INVENTION

In a manufacturing process of a semiconductor device or a liquid crystal display, a plasma processing apparatus such as a plasma etching apparatus or a plasma CVD apparatus has been used for performing a plasma process such as an etching process or a film forming process on a processing target substrate such as a semiconductor wafer or a glass substrate.

Recently, as such a plasma processing apparatus, a RLSA (Radial Line Slot Antenna) microwave plasma processing apparatus capable of uniformly generating high-density surface wave plasma having a low electron temperature is attracting attention (see, for example, Patent Document 1).

The RLSA microwave plasma processing apparatus includes a planar antenna (radial line slot antenna) having slots formed in a certain pattern. The planar antenna is provided in an upper portion of a chamber (processing vessel). Microwave induced from a microwave generation source through a coaxial waveguide is radiated into the chamber from the slots of the planar antenna. A gas introduced into the chamber is excited into plasma by a microwave electric field. Accordingly, a plasma process is performed on a processing target object such as a semiconductor wafer.

In order to adjust a plasma distribution in such a RLSA microwave plasma processing apparatus, it is required to provide a multiple number of antennas each having a different slot shape and pattern, and to exchange the antennas. In this case, processes become more complicated.

In order to solve this problem, described in Patent Document 2 is a microwave plasma source that splits microwave into a multiple number of microwaves, radiates the split microwaves into a chamber through a multiple number of antenna modules and combines the split microwaves in a space within the chamber.

As described above, by combining the microwaves in the space within the chamber by using the multiple number of antenna modules, phases or intensity of the microwaves radiated from the antennas of the antenna modules can be adjusted. As a result, the plasma distribution can also be adjusted.

Patent Document 1: Japanese Patent Laid-open Publication No. 2000-294550

Patent Document 2: Pamphlet of International Patent Publication No. 2008/013112

However, when the plasma is generated by radiating the microwaves into the chamber through the multiple number of antenna modules, antinodes and nodes of a standing wave generated when the microwaves are radiated into the chamber can occur. The antinodes and the nodes of the standing wave may cause non-uniformity of an electron density distribution in the plasma. As a result, a plasma density distribution may not become uniformized.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, the present disclosure provides a microwave plasma source capable of controlling positions of nodes and antinodes of a standing wave of microwave within the processing chamber not to be fixed and improving uniformity of a plasma density distribution within the processing chamber. Further, the present disclosure also provides a plasma processing apparatus using the microwave plasma source.

In accordance with a first aspect of the present disclosure, there is provided a microwave plasma source for introducing microwave into a processing chamber capable of performing a plasma process by exciting a gas supplied into the processing chamber into plasma by the microwave. The microwave plasma source includes a microwave generator for generating microwave; and a microwave supply unit configured to supply the generated microwave into the processing chamber. The microwave supply unit includes a multiple number of microwave introducing devices each introducing the microwave into the processing chamber; and a multiple number of phase controllers for adjusting phases of the microwaves input to the multiple number of microwave introducing devices. Here, the phases of the microwaves may be adjusted by fixing an input phase of the microwave input to one of two adjacent microwave introducing devices while varying an input phase of the microwave input to the other microwave introducing device according to a periodic waveform. Alternatively, the phases of the microwaves may be adjusted by varying input phases of the microwaves input to both of the two adjacent microwave introducing devices according to periodic waveforms not overlapped with each other.

The periodic waveform may be one of a sine waveform, a triangular waveform, a trapezoidal waveform and a waveform similar to a sine waveform.

Further, the microwave plasma source may further include a ceiling plate serving as a top wall of the processing chamber and configured to transmit the microwaves radiated from the multiple number of microwave introducing devices. Here, the ceiling plate may include a multiple number of dielectric members provided at positions corresponding to the multiple number of microwave introducing devices; and a metal frame, having a honeycomb structure, for supporting the dielectric members. The frame may have a gas flow path and a multiple number of gas discharge holes. Further, a gas used for the plasma process may be discharged into the processing chamber from the gas discharge holes.

In accordance with a second aspect of the present disclosure, there is provided a plasma processing apparatus including a processing chamber for accommodating therein a processing target substrate; a mounting table for mounting thereon the processing target substrate within the processing chamber; a gas supply unit for supplying a gas into the processing chamber; and the aforementioned microwave plasma source. Here, plasma may be generated by microwave introduced into the processing chamber from the microwave plasma source. Further, a process may be performed on the processing target substrate by the plasma.

In accordance with the present disclosure, the phases of the microwaves may be adjusted by fixing the input phase of the microwave inputted to one of two adjacent microwave introducing devices while varying the input phase of the microwave inputted to the other microwave introducing device according to the periodic waveform. Alternatively, the phases of the microwaves may be adjusted by varying input phases of the microwaves inputted to both of the two adjacent microwave introducing devices according to periodic waveforms not overlapped with each other. Accordingly, by continuously changing the positions of the nodes and the antinodes of the standing wave generated when the microwaves are radiated into the processing chamber, it may be possible to uniformize electric field intensity and to improve in-plane uniformity of the electric field intensity. As a result, an electron density, i.e., a plasma density within the processing chamber can be uniformized, and a uniform plasma process can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments will be described in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be intended to limit its scope, the disclosure will be described with specificity and detail through use of the accompanying drawings, in which:

FIG. 1 is a cross sectional view illustrating a schematic configuration of a surface wave plasma processing apparatus having a microwave plasma source in accordance with a first embodiment of the present disclosure;

FIG. 2 is a configuration view of the microwave plasma source;

FIG. 3 is a plane view schematically illustrating a microwave supply unit of the microwave plasma source;

FIG. 4 shows an example circuit configuration of a main amplifier of an antenna module of the microwave plasma source;

FIG. 5 is a cross sectional view illustrating a microwave introducing device of the antenna module of the microwave plasma source;

FIG. 6 is a transversal cross sectional view taken along a line AA′ of FIG. 5, and shows a power supply unit of the microwave introducing device;

FIG. 7 is a transversal cross sectional view taken along a line BB′ of FIG. 5, and shows a slug and a sliding member of a tuner;

FIG. 8 is a schematic diagram for describing a case where input phases of microwaves inputted to three microwave introducing devices among seven microwave introducing devices of the microwave plasma source are varied according to a periodic waveform;

FIG. 9 shows an input phase with time when an input phase of microwave inputted to one of adjacent microwave introducing devices is fixed to 0° while varying an input phase of microwave inputted to the other microwave introducing device according to a sine waveform;

FIGS. 10A to 10C show example periodic waveforms other than a sine waveform;

FIGS. 11A and 11B respectively show analysis results of electric field distributions within a chamber in a case where input phases of microwaves inputted to all of the seven microwave introducing devices of the microwave plasma source shown in FIG. 3 are set to be about 0° and in a case where input phases of microwaves inputted to three outer microwave introducing devices are changed by about 180°;

FIG. 12 is a plane view schematically illustrating a microwave supply unit and a ceiling plate of a microwave plasma source in accordance with a second embodiment of the present disclosure.

FIG. 13 is a cross sectional view taken along a line CC′ of FIG. 12;

FIG. 14 is a plane view schematically illustrating a modification example of the ceiling plate; and

FIG. 15 is a bottom view illustrating another modification example of the ceiling plate.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a cross sectional view illustrating a schematic configuration of a surface wave plasma processing apparatus having a microwave plasma source in accordance with a first embodiment of the present disclosure. FIG. 2 is a configuration view of the microwave plasma source. FIG. 3 is a plane view schematically illustrating a microwave supply unit of the microwave plasma source. FIG. 4 shows an example circuit configuration of a main amplifier of an antenna module of the microwave plasma source. FIG. 5 is a cross sectional view illustrating a microwave introducing device of the antenna module of the microwave plasma source. FIG. 6 is a transversal cross sectional view taken along a line AA′ of FIG. 5, and shows a power supply unit of the microwave introducing device. FIG. 7 is a transversal cross sectional view taken along a line BB′ of FIG. 5, and shows a slug and a sliding member of a tuner.

A surface wave plasma processing apparatus 100 is configured as a plasma etching apparatus that performs a plasma process such as an etching process on a wafer. The surface wave plasma processing apparatus 100 may include a substantially cylindrical chamber 1 and a microwave plasma source 2 for generating microwave plasma within the chamber 1. The chamber 1 is made of a metal material such as aluminum or stainless steel, and is airtightly sealed. Further, the chamber 1 is electrically grounded. An opening 1 a may be formed at a top portion of the chamber 1, and the microwave plasma source 2 is provided in the opening la so as to face the inside of the chamber 1.

A susceptor 11 for horizontally mounting thereon a wafer W as a processing target object is provided within the chamber 1. The susceptor 11 is supported on a cylindrical supporting member 12 that is provided at a center of a bottom of the chamber 1 via an insulating member 12 a. The susceptor 11 and the supporting member 12 may be made of, e.g., aluminum having an alumite-treated (anodically oxidized) surface.

Although not illustrated, if necessary, the susceptor 11 may include an electrostatic chuck for electrostatically attracting the wafer W, a temperature control device, a gas flow path for supplying a heat transfer gas to a rear surface of the wafer W and a vertically movable elevating pin for transferring the wafer W. Further, the susceptor 11 is electrically connected with a high frequency bias power supply 14 via a matching unit 13. A high frequency power is supplied to the susceptor 11 from the high frequency bias power supply 14, so that ions in the plasma may be attracted toward the wafer W.

A gas exhaust pipe 15 is connected to the bottom of the chamber 1, and a gas exhaust unit 16 including a vacuum pump is connected with the gas exhaust pipe 15. By operating the gas exhaust unit 16, the chamber 1 is evacuated, so that the inside of the chamber 1 can be depressurized to a certain vacuum level at a high speed. Furthermore, a loading/unloading port 17 for loading and unloading the wafer W and a gate valve 18 for opening and closing the loading/unloading port 17 are provided at a sidewall of the chamber 1.

A shower plate 20 for discharging a processing gas for plasma etching toward the wafer W is horizontally provided above the susceptor 11 within the chamber 1. The shower plate 20 includes a lattice-shaped gas flow path 21 and a multiple number of gas discharge holes 22 formed in the gas flow path 21. There exist spaces 23 between lattice patterns of the gas flow path 21. An outwardly extending pipe 24 is connected to the gas flow path 21 of the shower plate 20. The pipe 24 is connected with a processing gas supply source 25.

Further, a ring-shaped plasma gas introducing member is provided along the sidewall of the chamber 1 at a position above the shower plate 20 of the chamber 1, and a multiple number of gas discharge holes are formed at an inner periphery of the plasma gas introducing member 26. The plasma gas introducing member 26 is connected to a plasma gas supply source 27 for supplying the plasma gas via a pipe 28. A rare gas such as an Ar gas may be used as the plasma gas.

The plasma gas introduced into the chamber 1 from the plasma gas introducing member 26 is excited into plasma by the microwave introduced into the chamber 1 from the microwave plasma source 2. This plasma travels in the spaces 23 of the shower plate 20 and excites the processing gas discharged from the gas discharge holes 22 of the shower plate 20. As a result, plasma of the processing gas is generated.

The microwave plasma source 2 is provided on a ceiling plate 110 supported by a supporting ring 29 placed at the upper portion of the chamber 1. A gap between the supporting ring 29 and the ceiling plate 110 is hermetically sealed. As illustrated in FIG. 2, the microwave plasma source 2 includes a microwave output unit 30 for splitting and outputting microwaves and a microwave supply unit 40 for guiding and radiating the microwaves outputted into the chamber 1 from the microwave output unit 30.

The microwave output unit 30 includes a microwave power supply 31, a microwave oscillator 32, an amplifier 33 and a splitter 34. The amplifier 33 amplifies the oscillated microwave, and the splitter 34 splits the amplified microwave in plural numbers.

The microwave oscillator 32 oscillates microwave of a certain frequency (e.g., about 2.45 GHz), by way of example, by PLL (Phase Locked Loop). The splitter 34 splits the microwave amplified by the amplifier 33 while matching input impedance with output impedance so as to reduce a loss of the microwave. Here, the microwave may have a frequency other than about 2.45 GHz, e.g., about 8.35 GHz, about 5.8 GHZ, about 1.98 GHz or about 915 MHz.

The microwave supply unit 40 includes a multiple number of antenna modules 41 for introducing the microwaves split by the splitter 34 into the chamber 1. Each antenna module 41 includes an amplifier unit 42 for amplifying the split microwave and a microwave introducing device 43. Further, the microwave introducing device 43 includes a tuner 60 for matching impedances and an antenna unit 45 for radiating the amplified microwave into the chamber 1. The split microwave is radiated into the chamber 1 from the antenna unit 45 of the microwave introducing device 43 of each of the antenna modules 41. As depicted in FIG. 3, the microwave supply unit 40 includes seven antenna modules 41. Here, six microwave introducing devices 43 are annularly arranged on the circular ceiling plate 110, and one microwave introducing device 43 is provided at the center thereof. The ceiling plate 110 serves as a vacuum seal and a microwave transmitting plate. The ceiling plate 110 includes a metal frame 110 a and dielectric members 110 b provided at positions where the microwave introducing devices 43 are provided. Each dielectric member 110 b is made of a dielectric material such as quartz.

The amplifier unit 42 includes a phase controller 46, a variable gain amplifier 47, a main amplifier 48 as a solid state amplifier and an isolator 49.

The phase controller 46 is capable of changing a phase of microwave. By the phase controller 46, radiation property can be modulated. By way of example, by adjusting a phase of microwave for each antenna module, directivity can be controlled, and a plasma distribution can be varied. In the present embodiment, as will be described later, by fixing a phase of microwave of a certain antenna module while continuously varying a phase of microwave of an antenna module adjacent thereto, it is possible to suppress a standing wave of the microwave.

The variable gain amplifier 47 adjusts a power level of the microwave to be inputted to the main amplifier 48. Further, the variable gain amplifier 47 also regulates plasma intensity or controls a difference between the respective antenna modules. By adjusting the variable gain amplifier 47 for each antenna module, a certain plasma distribution may be generated.

As shown in FIG. 4, the main amplifier 48 as the solid state amplifier may include, for example, an input matching circuit 131, a semiconductor amplifying device 132, an output matching circuit 133 and a high Q resonance circuit 134.

The isolator 49 separates microwave reflected from the antenna unit 45 and heading toward the main amplifier 48. The isolator 49 includes a circulator and a dummy load (a coaxial terminator). The circulator sends the microwave reflected from the antenna unit 45 to the dummy load, and the dummy load converts the reflected microwave sent from the circulator into heat.

Now, the microwave introducing device 43 will be explained.

As depicted in FIGS. 5 and 6, the microwave introducing device 43 includes a coaxial waveguide 44 for transmitting microwave and the antenna unit 45 for radiating the microwave transmitted through the waveguide 44 into the chamber 1. Microwaves radiated from the respective microwave introducing devices 43 into the chamber 1 are combined within the chamber 1, so that surface wave plasma is generated within the chamber 1.

The waveguide 44 includes a cylindrical external conductor 52 and a rod-shaped internal conductor 53. The external conductor 52 and the internal conductor 53 are coaxially arranged. The antenna unit 45 is positioned at a leading end of the waveguide 44. In the waveguide 44, the internal conductor 53 serves as a power supply, while the external conductor 52 is electrically grounded. A reflection plate 58 is provided at upper ends of the external conductor 52 and the internal conductor 53.

A power supply device 54 for supplying the microwave (electromagnetic wave) is provided at a side of the waveguide 44. The power supply device 54 includes a microwave power inlet port 55 for introducing a microwave power. The microwave power inlet port 55 is provided at a side surface of the waveguide 44 (external conductor 52). The microwave power inlet port 55 is connected with a coaxial line 56 as a power supply line for supplying the microwave amplified by the amplifier unit 42. The coaxial line 56 includes an internal conductor 56 a and an external conductor 56 b. Further, a leading end of the internal conductor 56 a of the coaxial line 56 is connected to a power supply antenna 90 horizontally extending toward the inside of the external conductor 52.

The power supply antenna 90 may be, for example, formed as a microstrip line on a PCB substrate as a print circuit. Provided in a gap between the reflection plate 58 and the power supply antenna 90 is a wavelength shortening member 59 for shortening an effective wavelength of a reflection wave. The wavelength shortening member 59 may be made of a dielectric material such as Teflon (Registered Trademark). Here, when microwave having a high frequency of, e.g., about 2.45 GHz is used, the wavelength shortening member 59 may not be provided. Since the electromagnetic wave radiated from the power supply antenna 90 is reflected by the reflection plate 58, a maximum amount of electromagnetic wave can be transmitted into the coaxial waveguide 44. Here, a distance from the power supply antenna 90 to the reflection plate 58 may be set to be multiples of half-wavelength of λg/4.

As shown in FIG. 6, the power supply antenna 90 includes an antenna main body 91 and a reflection member 94. The antenna main body 91 includes a first pole 92 to which an electromagnetic wave is supplied and a second pole 93 for radiating the supplied electromagnetic wave. Further, the antenna main body 91 is connected to internal conductor 56 a of the coaxial line 56 at the microwave power inlet port 55. The reflection member 94 has a ring shape and is extended along the outside of the internal conductor 53 from the both sides of the antenna main body 91. In this configuration, the standing wave may be generated by the electromagnetic wave incident to the antenna main body 91 and the electromagnetic wave reflected from the reflection member 94. The second pole 93 of the antenna main body 91 is in contact with the internal conductor 53.

As the power supply antenna 90 radiates the microwave (electromagnetic wave), the microwave power is supplied into a space between the external conductor 52 and the internal conductor 53. The microwave power supplied to the power supply device 54 is propagated to the antenna unit 45.

Furthermore, the tuner 60 is provided in the waveguide 44. The tuner 60 is configured to match load (plasma) impedance within the chamber 1 with characteristic impedance of the microwave power supply in the microwave output unit 30. The tuner 60 includes two slugs 61 a and 61 b provided between the external conductor 52 and the internal conductor 53; and a slug driving unit 70 provided at the outside (top) of the reflection plate 58. Further, the slugs 61 a and 61 b are vertically movable along the waveguide 44.

Among these slugs, the slug 61 a is located on the side of the slug driving unit 70, while the slug 61 b is located on the side of the antenna unit 45. Two slug moving shafts 64 a and 64 b for moving the slugs are provided within an internal space of the internal conductor 53 in a lengthwise direction of the internal conductor 53. Each of the slug moving shafts 64 a and 64 b is formed of, e.g., a screw rod having a trapezoidal screw.

As shown in FIG. 7, the slug 61 a is made of a dielectric material and has a ring shape. A sliding member 63 made of resin having slidable property is fitted to the inside of the slug 61 a. The sliding member 63 has a screw hole 65 a into which the slug moving shaft 64 a is screwed; and a through hole 65 b through which the slug moving shaft 64 b is inserted. Like the slug 61 a, a sliding member 63 of the slug 61 b also has a screw hole 65 a and a through hole 65 b. However, unlike the slug 61 a, the slug moving shaft 64 b is screwed into the screw hole 65 a of the sliding member 63, and the slug moving shaft 64 a is inserted through the through hole 65 b of the sliding member 63. Accordingly, by rotating the slug moving shaft 64 a, the slug 61 a is moved up and down, and by rotating the slug moving shaft 64 b, the slug 61 b is moved up and down. That is, the slugs 61 a and 61 b are moved up and down by a screw device including the slug moving shafts 64 a and 64 b and the sliding members 63.

The internal conductor 53 has three slits 53 a arranged at a regular interval, and the three slits 53 a are formed in a lengthwise direction thereof. Further, each of the sliding members 63 has three protrusions 63 a arranged at a regular interval so as to correspond to the three slits 53 a, respectively. The sliding members 63 are respectively fitted into the slugs 61 a and 61 b while the protrusions 63 a are in contact with the inner peripheries of the slugs 61 a and 61 b. Outer peripheral surfaces of the sliding members 63 are firmly in contact with inner peripheral surfaces of the internal conductor 53. As the slug moving shafts 64 a and 64 b are rotated, the sliding members 63 are moved up and down while being slid on the internal conductor 53. That is, the inner peripheral surfaces of the internal conductor 53 serves as a sliding guide of the slugs 61 a and 61 b. By way of example, a width of each slit 53 a may be set to be equal to or smaller than about 5 mm. With this configuration, as will be described later, a microwave power that leaks into the internal conductor 53 can be substantially removed, and, thus, radiation efficiency of the microwave power can maintains high.

As the sliding member 63, resin that can be easily fabricated and has fine slidable property may be used. By way of example, polyphenylene sulfide (PPS) resin (Product name: BEAREE AS5000 (manufactured by NTN Co., Ltd.)) may be used.

The slug moving shafts 64 a and 64 b are extended to the slug driving unit 70 through the reflection plate 58. Although not shown, bearings are provided between the slug moving shafts 64 a and 64 b and the reflection plate 58. Further, a bearing 67 made of a conductor is provided at a lower end of the internal conductor 53, and lower ends of the slug moving shafts 64 a and 64 b are supported on the bearing 67.

The slug driving unit 70 has a housing 71. The slug moving shafts 64 a and 64 b are extended into the housing 71. Gears 72 a and 72 b are fixed to upper ends of the slug moving shafts 64 a and 64 b, respectively. Further, the slug driving unit 70 also includes a motor 73 a for rotating the slug moving shaft 64 a and a motor 73 b for rotating the slug moving shaft 64 b. A gear 74 a is fixed to a shaft of the motor 73 a, and a gear 74 b is fixed to a shaft of the motor 73 b. The gear 74 a is engaged with the gear 72 a, and the gear 74 b is engaged with the gear 72 b. With this configuration, the slug moving shaft 64 a is rotated by the motor 73 a via the gears 74 a and 72 a, and the slug moving shaft 64 b is rotated by the motor 73 b via the gears 74 b and 72 b. The motors 73 a and 73 b may be, e.g., stepping motors.

Moreover, the slug moving shaft 64 b is longer than the slug moving shaft 64 a such that the upper end of the slug moving shaft 64 b extends to a higher position than the upper end of the slung moving shaft 64 a. Accordingly, if the positions of the gears 72 a and 72 b are offset vertically, the motors 73 a and 73 b are also offset vertically. Thus, a space for power transmission units such as the motors and the gears can be reduced, and the housing 71 accommodating the power transmission units may have the same diameter as that of the external conductor 52.

Incremental encoders 75 a and 75 b for detecting positions of the slugs 61 a and 61 b are directly connected with output shafts of the motors 73 a and 73 b, respectively.

The positions of the slugs 61 a and 61 b are controlled by a slug controller 68. To elaborate, based on an impedance magnitude of an input terminal detected by a non-illustrated impedance detector and position information of the slugs 61 a and 61 b detected by the encoders 75 a and 75 b, the slug controller 68 controls the positions of the slugs 61 a and 61 b by sending a control signal to the motors 73 a and 73 b. Accordingly, the impedance can be adjusted. The slug controller 68 performs impedance matching such that impedance of a termination end becomes, e.g., about 50 Ω. If only one of the two slugs is moved, a trajectory passing through an origin on a Smith chart is created. If both slugs are moved, only a phase is rotated.

The antenna unit 45 includes a planar slot antenna 81 having slots 81 a and serving as a microwave radiation antenna. Further, the antenna unit 45 includes a wavelength shortening member 82 provided on a top surface of the planar slot antenna 81. A cylindrical member 82 a made of a conductor is provided through the center of the wavelength shortening member 82 so as to connect the bearing 67 with the planar slot antenna 81. Accordingly, the internal conductor 53 is connected with the planar slot antenna 81 via the bearing 67 and the cylindrical member 82 a. Further, a wavelength shortening member 83 is provided at a leading end side of the planar slot antenna 81. Further, a lower end of the external conductor 52 is extended up to the planar slot antenna 81, and an outside of the wavelength shortening member 82 is covered with the external conductor 52. Furthermore, outsides of the planar slot antenna 81 and the wavelength shortening member 83 are covered with a coating conductor 84.

Each of the wavelength shortening members 82 and 83 has a dielectric constant larger than that of a vacuum and is made of, e.g., quartz, ceramic, fluorine-based resin such as polytetrafluoroethylene, polyimide resin, or the like. In the vacuum, a wavelength of microwave may be lengthened. Accordingly, each of the wavelength shortening members 82 and 83 serves to shorten the wavelength of the microwave so as to reduce a size of the antenna. The wavelength shortening members 82 and 83 can adjust the phase of the microwave depending on their thicknesses. The thicknesses of the wavelength shortening members 82 and 83 may be adjusted such that the planar slot antenna 81 becomes a portion corresponding to an antinode of a standing wave. In this way, reflection of the microwave can be decreased, and radiation energy of the planar slot antenna 81 can be increased.

The wavelength shortening member 83 is in contact with the dielectric member 110 b inserted into the frame 110 a of the ceiling plate 110. The microwave amplified by the main amplifier 48 is transmitted to the space between the internal conductor 53 and the external conductor 52; passed through the wavelength shortening member 83 and the dielectric member 110 b of the ceiling plate 110 from the slots 81 a of the planar slot antenna 81; and radiated into the space within the chamber 1.

In the present embodiment, the main amplifier 48, the tuner 60 and the planar slot antenna 81 are located adjacent to each other. The tuner 60 and the planar slot antenna 81 form a lumped constant circuit existing within a ½ wavelength. Further, since a combined resistance of the planar slot antenna 81 and the wavelength shortening members 82 and 83 is set to be about 50 Ω, the tuner 60 can directly tune the plasma load. Accordingly, energy can be efficiently transferred to the plasma.

Each component of the surface wave plasma processing apparatus 100 is controlled by a control unit 120 having a microprocessor. The control unit 120 may include a storage unit, an input unit, a display, and so forth. The storage unit stores therein process sequences of the surface wave plasma processing apparatus 100 and process recipes as control parameters. The control unit 120 controls the plasma processing apparatus according to a selected processing recipe.

Now, an operation of the surface wave plasma processing apparatus 100 having the above-described configuration will be explained. First, the wafer W is loaded into the chamber 1 and is mounted on the susceptor 11. Then, a plasma gas, e.g., an Ar gas is introduced into the chamber 1 from the plasma gas supply source 27 through the pipe 28 and the plasma gas introducing member 26, and microwave is introduced into the chamber 1 from the microwave plasma source 2. Accordingly, surface wave plasma is generated within the chamber 1.

After the surface wave plasma is generated, a processing gas, e.g., an etching gas such as a Cl₂ gas is discharged from the processing gas supply source 25 into the chamber 1 via the pipe 24 and the shower plate 20. The discharged processing gas is excited into plasma by the plasma that has passed through the spaces 23 of the shower plate 20. By using the plasma of the processing gas, a plasma process such as an etching process is performed on the wafer W.

When the surface wave plasma is generated, in the microwave plasma source 2, a microwave power oscillated by the microwave oscillator 32 of the microwave output unit 30 is amplified by the amplifier 33, and the amplified microwave power is split by the splitter 34 in plural numbers. Then, the split microwave powers are sent to the microwave supply unit 40. In the microwave supply unit 40, the split microwave powers are individually amplified by the main amplifiers 48 as the solid state amplifiers, and are supplied into the waveguides 44 of the microwave introducing devices 43, respectively. In each of the waveguides 44, impedances of the split microwave powers are automatically matched by the tuner 60. Then, without power reflection, the microwave powers are radiated into chamber 1 via the wavelength shortening member 82, the planar slot antenna 81, the wavelength shortening member 83 and the dielectric member 110 b of the ceiling plate 110. Then, the split microwave powers are combined within the chamber 1.

At this time, when an input phase of each microwave inputted into the microwave introducing device 43 is fixed to, e.g., about 0°, positions of nodes and antinodes of a standing wave generated when the microwave is radiated into the chamber 1 are fixed. Accordingly, electron density of the plasma may be non-uniform, resulting in deterioration of uniformity of a plasma density distribution.

To solve the problem, in the present embodiment, an input phase of the microwave inputted to one of two adjacent microwave introducing devices 43 is fixed, while varying an input phase of the microwave inputted to the other microwave introducing device 43 according to a periodic waveform such as a sine waveform. Alternatively, input phases of the microwaves inputted to both of the two adjacent microwave introducing devices 43 may be varied according to periodic waveforms not overlapped with each other.

By way of example, input phases of the microwaves inputted to three microwave introducing devices 43 marked by slanting lines of FIG. 8 are varied according to a periodic waveform, while fixing input phases of the microwaves inputted to the rest microwave introducing devices 43 marked by a white color to about 0°. Here, if the periodic waveform is set to be a sine waveform, the input phases of the microwaves inputted to two adjacent microwave introducing devices 43 are as shown in FIG. 9. Further, antinodes of a standing wave when the input phases of the microwaves inputted to the two adjacent microwave introducing devices 43 are all fixed to about 0° are changed nodes if the input phase of the microwave inputted to one of the adjacent microwave introducing devices 43 is varied by about 180°, or vice versa. In this way, by periodically varying the input phases of the microwaves, the positions of the nodes and the antinodes of the standing wave may be varied continuously, so that electric field intensity can be uniformized, and uniformity of the electric field intensity on a wafer surface can also be improved. Accordingly, electron density, i.e., plasma density within the chamber 1 can be uniformized, so that a uniform plasma process can be performed.

At this time, the phase of the microwave inputted to each microwave introducing device 43 may be adjusted by the phase controller 46 of each antenna module 41. Each phase controller 46 is controlled by the control unit 120.

The periodic waveform may not be limited to the sine waveform. By way of example, a triangular waveform as shown in FIG. 10A or a trapezoidal waveform as shown in FIG. 10B may be used. Moreover, the periodic waveform may not be limited to a perfect sine waveform. For example, in order to increase time during which a phase is about 180°, there may be used a waveform similar to a sine waveform (an analogous sine waveform) obtained by flattening a sine waveform at a phase around about 180°, as shown in FIG. 10C. Further, although a rectangular waveform may be also applicable, the rectangular waveform is not desirable because there is a portion where a differential value becomes infinite.

Actually, by using the microwave plasma source including seven microwave introducing devices as shown in FIG. 3, an electric field distribution within the chamber is investigated for each of cases where the input phases of the microwaves inputted to all the microwave introducing devices are fixed to about 0° and where three microwave introducing devices among six outer microwave introducing devices are changed by about 180°. Here, a pressure within the chamber is set to be about 0.5 Torr and a microwave power is set to be about 200 W. The result is shown in FIGS. 11A and 11B. FIG. 11A shows an electric field distribution when the input phases of the microwaves inputted to all the microwave introducing devices are fixed to about 0°. FIG. 11B shows an electric field distribution when the input phases of the microwaves inputted to the three outer microwave introducing devices are changed by about 180°. In FIGS. 11A and 11B, electric field intensity is indicated by different colors (black and white). In FIG. 11A, bright circular ring-shaped portions indicate portions where the electric field intensity is high around the microwave introducing devices of the antenna modules. These portions correspond to antinodes of the standing wave. Further, among these portions, darker portions represent higher electric field intensity. Furthermore, portions between the adjacent microwave introducing devices show lower electric field intensity. These portions correspond to nodes of the standing wave. Specifically, portions surrounded by a dashed line in FIG. 11A correspond to the nodes of the standing wave. Further, by changing the input phases of the microwaves inputted to the three microwave introducing devices by about 180°, the electric field intensity changes greatly, as shown in FIG. 11B. The portions, surrounded by the dashed line in FIG. 11A, correspond to the nodes of the standing wave. However, these portions are changed to the antinodes of the standing wave in FIG. 11B since the electric field intensity has been increased by changing the input phase of the microwave inputted to one of two adjacent microwave introducing devices by about 180°. That is, when the input phases of the microwaves inputted to all the microwave introducing devices 43 are fixed to about 0°, portions between adjacent microwave introducing devices 43 correspond the nodes of the standing wave. However, by changing the input phases of the microwaves inputted to the three outer microwave introducing devices 43 by about 180°, these portions are changed to correspond the antinodes of the standing wave. Based on this analysis, it can be understood that by varying the input phases periodically, the positions of the nodes and the antinodes of the standing wave can be continuously changed and electric field intensity can be uniformized. As a result, plasma density obtained by the electric field can also be uniformized.

In accordance with the present embodiment, among the multiple number of microwave introducing devices 43, the input phase of the microwave inputted to one of two adjacent microwave introducing devices is fixed, while varying the input phase of the microwave inputted to the other microwave introducing device according to the periodic waveform such as a sine waveform. Alternatively, the input phases of the microwaves inputted to both of the two adjacent microwave introducing devices 43 may be varied according to periodic waveforms not overlapped with each other. However, all of the microwave introducing devices need not satisfy these conditions. By way of example, among sets of two adjacent microwave introducing devices 43, only a part of these sets may satisfy these conditions.

Second Embodiment

Now, a second embodiment of the present disclosure will be described.

Although basic configurations of a microwave plasma source and a plasma processing apparatus in accordance with the second embodiment are the same as those of the first embodiment, a ceiling plate has a different configuration.

FIG. 12 illustrates a plane view schematically illustrating a ceiling plate and a microwave introducing device of a microwave plasma source in accordance with the second embodiment. FIG. 13 is a cross sectional view taken along a line CC′ of FIG. 12. As shown in FIGS. 12 and 13, a circular ceiling plate 110 in accordance with the second embodiment includes dielectric members 110 b fitted to positions where a multiple number of microwave introducing devices 43 for radiating microwaves into the chamber 1 are provided. Each dielectric member 110 b is made of a dielectric material such as quartz and has a hexagon shape. Adjacent dielectric members 110 b are placed close to each other such that one side of a hexagon faces to one side of other hexagon. A metal frame 110 a supporting the dielectric members 110 b has a honeycomb structure. Portions of the metal frame 110 a between the adjacent dielectric members 110 b have narrow straight lines shapes. The frame 110 a has supporting members 110 c for supporting the dielectric members 110 b.

The ceiling plate 110 serves to transmit the microwaves as stated above. In order to transmit the microwave efficiently, the entire ceiling plate 110 may be made of a dielectric material. However, when the microwaves are radiated from the multiple number of microwave introducing devices 43 as in the microwave plasma source in accordance with the present embodiment, if the entire ceiling plate 110 is made of the dielectric material such as quartz, all the microwaves radiated from a certain microwave introducing device 43 may not be introduced into the chamber 1 but a part of the microwaves may reach another microwave introducing device 43 through the ceiling plate 110. In such a case, the microwave radiated from the certain microwave introducing device 43 and the microwave radiated from the another microwave introducing device 43 may interfere with each other. Further, if the entire ceiling plate 110 is made of the dielectric material, there may also be various other problems. By way of example, a mode jump of plasma may occur easily or strength of a dielectric member may become decreased.

For these reasons, in the ceiling plate 110 in accordance with the first embodiment, the dielectric members are provided only at positions where the microwave introducing devices 43 of the antenna modules 41 are placed, and other portions of the ceiling plate 110 have the metal frame for supporting the dielectric members. Each dielectric member may have a circular shape as in the first embodiment or may have a rectangular shape or a square shape.

If the dielectric members have circular shapes, however, the area of metal frame between the adjacent dielectric members would be increased and, thus, area occupied by the dielectric members may be reduced. In such a case, a microwave radiation area may also be reduced, making it difficult to generate plasma efficiently. Furthermore, when the dielectric members have rectangular shapes or square shapes, strength of the ceiling plate 110 may be decreased.

In contrast, as in the second embodiment, by forming the frame 110 a of the ceiling plate 110 to have the honeycomb structure and the dielectric members 110 b to have the hexagon shapes, the area of the ceiling plate 110 occupied by the dielectric members 110 b can be increased. Thus, the microwave radiation area can be increased and the plasma can be generated efficiently. Furthermore, by forming the frame 110 a to have the honeycomb structure, the strength of the ceiling plate 110 can be increased.

Although the frame 110 a is described in FIG. 12 to have the honeycomb structure, the frame 110 a may not have a perfect honeycomb structure but it may have a structure similar to the honeycomb structure. By way of example, as illustrated in FIG. 14, outer peripheries of the dielectric members 110 b corresponding to outer microwave introducing devices 43 may be protruded outward. In such a configuration, the areas of the dielectric members 110 b can be more increased. As described above, in accordance with the second embodiment, the frame 110 a may have a honeycomb structure and a honeycomb-shaped structure including a structure similar to the honeycomb structure.

As depicted in FIG. 15, a multiple number of gas discharge holes 112 may be formed at the frame 110 a of the ceiling plate 110 so as to discharge a plasma gas such as an Ar gas, as in a shower device. In such a case, a gas flow path may be formed inside the frame 110 a of the ceiling plate 110, and the plasma gas supply source 27 may be connected to the gas flow path via, e.g., the pipe 28. In this configuration, the plasma gas such as the Ar gas may be uniformly discharged from the gas discharge holes 112. Accordingly, the Ar gas can be excited into plasma promptly, so that uniform plasma can be generated.

Moreover, the effects of the second embodiment can be more enhanced when the second embodiment is combined with the first embodiment. However, the aforementioned effects of the second embodiment can be achieved even if the first embodiment is not combined.

Further, the present disclosure may not be limited to the above-described embodiment and can be modified in various ways. By way of example, the circuit configuration of the microwave output unit, or the circuit configuration of the microwave supply unit and the main amplifier may not be limited to the above-described embodiments. In addition, the microwave introducing device may also not be limited to those described in the embodiments. The microwave introducing device may have various configurations as long as it can radiate a microwave appropriately. Moreover, the number or the arrangement of the microwave introducing devices may not be limited to the above embodiments.

Further, in the above-described embodiments, the etching apparatus is used as the plasma processing apparatus. However, the present disclosure is not limited thereto and may be applicable to various other plasma processes such as a film forming process, an oxynitriding process, an asking process or the like. Furthermore, the processing target substrate is not limited to the semiconductor wafer, and various other types of substrates such as a FPD (Flat Panel Display) represented by an LCD (Liquid Crystal Display) and a ceramic substrate may be adopted. 

1. A microwave plasma source for introducing microwave into a processing chamber capable of performing a plasma process by exciting a gas supplied into the processing chamber into plasma by the microwave, the microwave plasma source comprising: a microwave generator for generating microwave; and a microwave supply unit, configured to supply the generated microwave into the processing chamber, including: a plurality of microwave introducing devices, each introducing the microwave into the processing chamber; and a plurality of phase controllers for adjusting phases of the microwaves input to the plurality of microwave introducing devices, wherein the phases of the microwaves are adjusted by fixing an input phase of the microwave input to one of two adjacent microwave introducing devices while varying an input phase of the microwave input to the other microwave introducing device according to a periodic waveform, or by varying input phases of the microwaves input to both of the two adjacent microwave introducing devices according to periodic waveforms not overlapped with each other.
 2. The microwave plasma source of claim 1, wherein the periodic waveform is one of a sine waveform, a triangular waveform, a trapezoidal waveform and a waveform similar to a sine waveform.
 3. The microwave plasma source of claim 1, further comprising: a ceiling plate serving as a top wall of the processing chamber and configured to transmit the microwaves radiated from the plurality of microwave introducing devices, wherein the ceiling plate includes: a plurality of dielectric members provided at positions corresponding to the plurality of microwave introducing devices; and a metal frame, having a honeycomb structure, for supporting the dielectric members.
 4. The microwave plasma source of claim 3, wherein the frame has a gas flow path and a plurality of gas discharge holes, and a gas used for the plasma process is discharged into the processing chamber from the gas discharge holes.
 5. A plasma processing apparatus comprising: a processing chamber for accommodating therein a processing target substrate; a mounting table for mounting thereon the processing target substrate within the processing chamber; a gas supply unit for supplying a gas into the processing chamber; and a microwave plasma source as claimed in claim 1, wherein plasma is generated by microwave introduced into the processing chamber from the microwave plasma source and a process is performed on the processing target substrate by the plasma. 